How to enable multiple selection for 'Display change request' screen

Hi, need insight on the below 3 queries

1. In Display Change Request screen, how could we enable multiple selection? As shown in the below image, i would need to select multiple records from  the F4 help.

2. Need to assign Custom search help to the field - 'Change Request' in the above screen. Which would be the best place to assign the search help?

     Is it to the field in table USMD120C or at webdynpro level (if so where exactly it is feasible)?

3. The multiple selection for 'Type of change request' field is enabled when checked in SE16, table USMD120C:

The same option is not available in UI:

Is there any standard way to enable this option in UI?

Thank you!